378 SOILS: PROPERTIES AND MANAGEMENT 



284. Removal of bases by drainage as a cause for 

 acidity. — The most potent cause of acid soils is doubt- 

 less the removal of bases in drainage water. The quan- 

 tities of basic material that may be lost from an acre of 

 soil are shown elsewhere (pars. 278, 279). These bases are 

 removed largely as bicarbonates, being obtained from 

 the hydrated aluminium silicates and other colloidal 

 matter. When the soil is uncropped a considerable loss 

 of lime occurs in the form of nitrate. As the decom- 

 position of the organic matter of the soil always results 

 in the formation of carbon dioxide and nitric acid, and 

 as decomposition is continually going on except when the 

 temperature of the soil becomes too low to admit of it, 

 the drain of bases from the soil is almost continuous. 

 Formation of carbon dioxide and of nitric acid occurs 

 largely in the surface soil ; consequently the removal 

 of bases begins there. The result is that soils are 

 likely to contain less calcium in the surface layers than 

 at lower depths. Ames and Gaither 1 have shown from 

 a large number of analyses of Ohio soils that those con- 

 taining calcium carbonate in appreciable quantities have 

 more calcium in the subsoil than in the surface six 

 inches. In other soils this was not uniformly the case. 

 Leaching is, of course, greater in amount where con- 

 siderable quantities of calcium carbonate are present 

 than where it is lacking. 



285. Removal of bases by plants. — Plants always 

 remove more bases than acids from soils in the process 

 of their growth. The table in paragraph 339 showing the 

 composition of the ash of some crops indicates that the 

 calcium, potassium, and magnesium removed from 



1 Ames, J. W., and Gaither, E. W. Soil Investigations. 

 Ohio Agr. Exp. Sta., Bui. 261. 1913. 



